Etching media comprising hydrofluoric acid, in particular hydrofluoric acid vapor, are frequently used in microsystems technology for so-called sacrificial layer etching, wherein micromechanical structures on a silicon oxide layer are rendered freely movable by undercutting. The advantage of the use of hydrofluoric acid vapor is that, as a result of the “semi-dry” procedure, so-called sticking, that is to say irreversible adhesion of the completely undercut structures to the substrate or to other structural parts, can be prevented.
Document US 2002/0106865 A1 describes a method of forming a shallow trench isolation. In such a method, a second oxide is selectively deposited from the liquid phase onto the surface of a first oxide using an oversaturated aqueous fluorosilicic acid solution, in which the deposition takes place.
From document U.S. Pat. No. 5,453,395 there is further known a method of forming an isolation structure on a silicon substrate, in which a selective deposition of an oxide only in trenches of the substrate is to be carried out.